1. Field of the Invention
The present invention relates to a method for manufacturing tires, and more particularly to a process of assembling constituent elements of a motorcar tire.
2. Description of the Prior Art
A radial tire 01 manufactured through a method in the prior art is shown in cross-section in FIG. 7. A carcass ply 02 lined with an inner liner which forms an inner surface of a tire is subjected to shaping into a toroidal form. Both side portions of the carcass ply 02 are covered by side walls 03, and a crown portion is surrounded by a BT-band 06 consisting of a belt 04 and a top tread 05. In a shoulder portion extending from the side portion to the crown portion is embedded a cushion rubber member 07.
Next, brief description will be made on one example of heretofore known methods for manufacturing such radial tires 01 (Official Gazette of Laid-Open Japanese Patent Specification No. 59-124408 (1984)) with reference to FIG. 8 through FIG. 11.
First, the carcass ply 02 is applied onto a first drum 010 as extended from the drum to the both sides, it is folded a little to portions corresponding to the drum ends along the edges of the drum. Beads 08 are then inserted into the folded portions (See FIG. 8)
The extended portions on the respective sides of the carcass ply 02 are folded back so as to wrap around these beads 08, and side walls 03 are applied as covering the folded-back portions to form a base green case (See FIG. 9). It is to be noted that at the end portions of the side walls 03 are preset cushion rubber members 07.
Thereafter, the base green case is extracted by reducing the outer diameter of the first drum 010 and is placed on a second drum assembly 011 as shown in FIG. 10. The second drum assembly 011 is composed of a pair of left and right drum bodies opposed to each other along their axial direction.
The BT-band 06 is preliminarily formed by sequentially wrapping first to third (or more) belts around a BT-drum as superposed on one another and further sticking a top tread 05 thereto in superposition. The thus formed BT-band 06 is extracted from the BT-drum by reducing the outer diameter of the BT-drum, and is positioned concentrically with the outer circumference of the base green case set on the above-mentioned second drum assembly 011.
Subsequently, the left and right drum bodies of the second drum assembly 011 are made to approach each other and air is made to flow into the space between the two drum bodies. Then the central portion of the carcass ply 02 will expand outwards (See FIG. 10), and eventually the carcass ply 02 would deform into a toroidal shape and also would join with the BT-band 06 (See FIG. 11).
In this way a green tire is manufactured, subsequently is loaded in a tire vulcanizing machine and hardened, and thereby a radial tire 01 as shown is FIG. 1 is obtained.
However, since expansion of the base green case shown in FIG. 11 presents an extremely large expansion of about 200%, there is a fear that the cushion rubber members 07 bonded to the carcass ply 02 may peel off or elongation of the cushion rubber members 07 may not be effected uniformly and unevenness in thickness may arise.
In addition, when thick members such as the cushion rubber members 07 are bonded to the carcass ply 02 at laterally symmetric positions and made to expand jointly with the carcass ply, there is a problem that due to different expansion rates between the left side and the right side caused by unevenness in thickness of the cushion rubber members 07, the base green case may expand in a distorted shape. So there is a disadvantage that deviation may arise also in the sticking position of the BT-band.
Furthermore, since the steps of folding the side walls 03, bonding, transferring the base green case from the first drum 010 to the second drum assembly 011 and expanding the same must be effected sequentially, high productivity cannot be expected.